Antenna with translational and rotational compensation



Sept. 1, 1970 T. E. PLUNK ET AL 3,526,898

ANTENNA WITH TRANSLATIONAL AND ROTATIONAL COMPENSATION Filed April 5, 1967 L F rm /6 22 I Z I LINEAR VARIABLE l POWER i ARRAY DIVIDER i 40 48 R BLE VA IA 2 VQEIAASBELE 46 38 PHASE HIFTER T: 1 SHIFTER 56 MAGIC'T VARIABLE H65 SHI VARIABLE POWER 20 DIVIDER /& I

ggwgg L CIRCULATOR\58 F/G. 6 DIVIDER C N62 TRANSM|TTER .Lcmcugwon nwavrons I \64 mar E. PLU/VK RECE Iv ER mar/mm smwsar F/G 7 BY M 27, Q2... ATTORNEY United States Patent O U.S. Cl. 343-771 6 Claims ABSTRACT OF THE DISCLOSURE An antenna for a radar system comprising a linear phased array having two diiferent edge slotted linear arrays which are interleaved, and a variable power divider which varies the phase and amplitude of the drive power to the arrays.

BACKGROUND OF THE INVENTION Field of the invention The invention pertains to moving radar systems such as groundborne, seaborne, or airborne systems.

Description of the prior art One previous technique processes the sum and difference patterns from phase and amplitude monopulse sys tems in the receiver at intermediate frequency in order to provide compensation. However, this compensation is not precise and is not achieved during both transmit and receive.

The prior art describing interleaped planar arrays does not teach arrays which provide compensation.

SUMMARY OF THE INVENTION An antenna having translational and rotational compensation comprising a linear phased array having two interleaved radiators with one radiator producing a sine illumination function and the other producing a cosine illumination function.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the inventive antenna;

FIG. 2 is a diagrammatic representation of the linear phased array;

FIG. 3 is a diagrammatic representation of a portion of a radiator;

FIG. 4 is a diagrammatic representation of coupling waveguides;

FIG. 5 is a block diagram of a variable power divider;

FIG. 6 is a block diagram showing the operation of the variable power divider when there is compensation for receive only; and

FIG. 7 is a block diagram showing the operation of the variable power divider when there is compensation for transmit only.

DESCRIPTION OF THE PREFERRED EMBODIMENT A block diagram of the inventive antenna 10 is shown in FIG. 1 and comprises linear phased array 14 connected to variable power divider 20. During receive operation, a target echo is received on line 12 and passes into linear phased array 14. The signals produced by linear phased array :14 are passed to variable power divider via lines 16 and 18. However, during transmit operation, variable power divider 20 applies signals to the waveguides represented by lines 16 and 18 which then enter linear phased array 14. Linear phased array 14 then transmits signals into space via line 12.

3,526,898 Patented Sept. 1, 1970 "Ice 1 where d =the length of the linear arrays d=the angle measured from a perpendicular to the face of the array and in the plane of the long dimension Such an antenna has wide application in the field of airborne radars where it is desirable to compensate for the forward motion of the platform or aircraft, and the rotation of the antenna while scanning. The translational displacement of the phase center of linear phased array 14 gives the effect of lifting antenna 10 and sliding it over. The phase center of linear phased array 14 is the point about which there is a constant phase at a constant radius. The rotation of the far field antenna pattern gives the elfect of physically rotating antenna 10.

Linear phased array 14 is diagrammatically shown in FIG. 2 and comprises two different linear arrays 24 and 26 which are interleaved and selectively coupled to coupling waveguides 16 and 18 shown in detail in FIG. 4. Linear array 24 produces a cosine illumination function, while linear array 26 produces a sine illumination func tion. Accordingly, the amplitude and phase magnitude of energy generated by array 24 is in the form of a cosine waveform, whereas the energy generated by array 26 is in the form of a sine waveform. By varying the phase and amplitude of the drive power to each array 24 and 26 using variable power divider 20 which will be described in detail later, it is possible to compensate for the forward motion of a platform and antenna rotation.

In order to best describe the inventive antenna 10, a physical description thereof is being given first and will be followed by its mathematical analogy. Linear phased array 14 comprises a set of stacked, edge slotted linear radiators wherein every other radiator 24 has a cosine illumination function, and the intervening radiators 26 have a sine illumination function. These current distributions are obtained by selectively varying the angle of inclination of the slots 28, which is a Well-known technique. For example, it is described in Massachusetts Institute of Technology Radiation Laboratory Series, published by McGraw-Hill Book Company Inc., 1949, Volume 12, chapter 9, wherein it is shown that an edge slot in the narrow wall of a rectangular waveguide (for example, FIG. 9.17(e) of the referenced text) can be represented by a simple shunt equivalent circuit having a conductance g given by the relationship in which and A are respectively the free space and guide wavelengths of the radiation, a and b are respectively the broad and narrow wall widths, and 6 is the angle of inclination of a slot (0:0 corresponding to a slot perpendicular to the edge of the waveguide). The power radiated from such a slot is proportional to the conductance g and accordingly, the power and the magnitude of the electric field radiated from each of a series of such slots is selected by choosing the slot angle from the foregoing equation, that is incorporated herein by reference. FIG. 3 depicts a portion of a sample radiator 30 having slots 28 shown in more detail. Radiator 30 comprises -a waveguide, and slots 28 are rectangular in shape. Nevertheless, other shapes may be used in order to achieve the desired illumination function. Slots 28 are cut into side 32 of radiator 30 and extend the whole width of side 32. There are no slots in the other sides of radiator 30.

In FIG. 2, lines 16 and 18 represent waveguides, and lines 17 and 19 represent holes therein. These waveguides are shown in detail in FIG. 4, and would be arranged parallel to each other and each being flush with ends 34 of linear arrays 24 and 26. Waveguide 16 affords coupling for linear arrays 24 which generate a cosine illumination function. Each hole 17 is arranged to be positioned at end 34 of one linear array 24 in order to provide the coupling thereto. Similarly, waveguide 18 affords coupling for linear arrays 26 which generate a sine illumination function. Every hole 19 is arranged to be positioned at end 34 of one linear array 26 to provide the coupling thereto. Hence, waveguides 16 and 18 are located perpendicular to linear arrays 24 and 26.

Variable power divider 20 is depicted in FIG. and comprises variable phase shifter 36 connected to waveguide magic-T 38; waveguide magic-T 44; and, variable phase shifters 40 and 42 connected between magic-T 38 and magic-T 44. Variable phase shifters 36, 40, and 42 may comprise ferrite digital latching phase shifters. The phase and amplitude of the power fed to linear phased array 14 is supplied by variable power divider and particularly by variable phase shifters 36, 40, and 42. Magic-T 38 is of conventional form and as is well known, signals entering the pair of arms 48 and 50, in phase, exit through the sum arm (H plane arm), while signals entering the pair of arms 48 and 50, antiphased, exit through the difference arm ('E plane arm). At intermediate phase relationships, the sum of these two signals splits between the sum and difference arms. Thus, the power entering magic-T 38 via arms 48 and 50 is divided between the arms 16 and 46 in accordance with the relative phase shifts applied by the variable phase shifters 40 and 42. Variable phase shifter 36 provides the desired phase shift between signals entering linear arrays 24 and 26. During receive operation, waveguide 18 which is coupled to linear array 26 receives sine illumination energy and applies it to variable phase shifter 36 that shifts its phase before applying the energy to magic-T 38 via line 46. In addition, waveguide 16 which is coupled to linear array 24 applies cosine illumination energy to magic-T 38. Magic-T 38 couples the sine illumination energy from variable phase shifter 36 to variable phase shifter 42, and the cosine illumination energy from waveguide 16 to variable phase shifter 40. Variable phase shifter 40 shifts the phase of the cosine illumination energy and applies the energy to magic-T 44, while variable phase shifter 42 shifts the phase of the sine illumination energy and applies the energy to magic-T 44 which then couples the energy to a receiver (not shown).

During transmit operation, variable power divider 20 operates in the opposite direction in order to couple energy to cosine linear array 24 and sine linear array 26 from a transmitter (not shown). Magic-T 44 selectively applies energy to variable phase shifters 40 and 42 which shift the phase of their input energy. The energy from ariable phase shifter 40 and variable phase shifter 42 is next applied to magic-T 38 which selectively applies energy to variable phase shifter 36 and to waveguide 16 that is coupled to cosine linear arrays 24. Variable phase shifter 36 shifts the phase of the received energy and applies the energy to waveguide 18 which is coupled to sine linear arrays 26. Although one embodiment of variable power divider 20 has been described, it should be appreciated that other embodime t r p s ible.

In the foregoing description, compensation for the forward motion of a platform and antenna rotation was performed during both receive and transmit operations. However, it is also possible to compensate only during receive or only during transmit operation. FIG. 6 depicts the operation of variable :power divider 20 when there is compensation for receive only. Hence, during receive operation, waveguide 18 which is coupled to sine linear arrays 26 applies energy to variable power divider 20. Waveguide 16 which is coupled to cosine linear arrays 24 applies energy to circulator 58 that may be a ferrite circulator and that in turn transfers this energy to variable power divider 20. Upon transmit operation, transmitter 60 transmits energy to circulator 58 which then applies it to waveguide 16. Since waveguide 16 is coupled to linear arrays 24, only the cosine linear arrays 24 receive energy during transmit operation.

FIG. 7 depicts the operation of variable power divider 20 when there is compensation for transmit only. Thus, during receive operation, waveguide 16 which is coupled to linear array 24 applies cosine energy through circulator 62 to receiver 64. Consequently, receiver 64 obtains only cosine energy during receive operation. Upon transmit operation, variable power divider 20 applies energy to waveguide 18 which is coupled to sine linear arrays 26. In addition, variable power divider 20 transfers energy to circulator 62 which then applies it to waveguide 16 that is coupled to cosine linear arrays 24.

As was mentioned previously, linear phased array 14 is compensated in order to cause the electrical phase center to be moved linearly in addition to rotating the far field pattern. This can be easily illustrated mathematically by first considering the total aperture function in the long dimension of the array for the translational case alone. This function is as follows:

where x=the dimensional variable along the length of array 14 a=length of array 14 k =a constant which determines the amount of translation For the case of rotation alone, the total aperture function can be written:

where k =a constant which is not equal to k and determines the degree of rotation Equations 2 and 3 may be restated in different form so that for translation m) (1+k1 cos +tank (4) and for rotation For small values of k; and x, Equation 5 may be approximated by In the usual case where translation and rotation are which is mathematically equivalent to,

/1+k cos (%+tan- In) For comparatively small k k and x, Equation 8 can be approximated by,

xei tan-l 8 1r5l3 VFW a (9) Since the amplitude of f(x) is small as x approaches a/2, the previous approximations (8) and (9) are valid for every allowable x, i.e. [xlga/Z. Consequently, Equations 7, 8, and 9 for f(x) are defined over Ixlga/Z and are zero for ]x[ a/2.

Note that in the case of translation as described by Equation 4 a term, tan k has appeared in the cosine portion. This means that the addition of the sine to the cosine illumination merely produces a shift in the origin of the function without changing its shape. In other words, array 14 appears to have physically translated through a small linear displacement equal to a can- 701 1r In the case of rotation, it is necessary to utilize the Fourier transform pair relationship between the aperture distribution function and the far field antenna pattern as follows:

sin

where \=the operating wavelength 0=the angle measured from a perpendicular to the face of the array and in the plane of the long dimension Substituting the aperture function for the rotational case in this transform relationship:

sin-

occurs which is equivalent to a small angular displacement or rotational of the far field pattern.

The far field pattern with both translational and rotational compensation is approximately the last Equation 13 for the far field pattern provides an aperture translation of x =a/1r tank and an angular rotation of Hence, it is possible to control the amount of rotation and translation by varying the constants k and k As was mentioned previously, the invention which precisely compensates for the displacement of the platform as well as the rotation of the antenna during scanning has application in airborne radar systems such as pulsed doppler radars where it is desirable in order to prevent distributed target, i.e. ground or sea clutter, spectrum broadening. Such compensation is possible on both transmit and receive. Other radar systems such as side looking radars, airborne fire control, shipborne, truck or tank mounted radars may be improved by using this invention.

Although the invention has been described with reference to a preferred embodiment thereof, it should be appreciated that it is not limited thereby. For instance, the interleaved radiators are not limited to those which generate sine and cosine functions and can produce other combinations of plus and minus functions. Hence, the invention must be given the full scope of the following claims.

What we claim is:

1. An antenna system supported by a moving platform and providing compensation for the movement of the platform, the antenna system comprising:

a first array having an odd illumination function;

a second array, interleaved with the first array, and

having an even illumination function; and

variable power divider means adapted to receive power from a transmitter, and communicating a portion of the power to the first array and a second portion of the power to the second array to displace the center of the sum of the odd and the even illumination functions.

2. An antenna system supported by a moving platform and providing compensation for the movement of the platform, the antenna system comprising:

a first array adapted to transmit power and having an odd illumination function;

a second array adapted to transmit power, interleaved with the first array, and having an even illumination function; and

variable phase shifting means for varying the phase of power transmitted by the first array relative to the phase of power transmitted by the second array whereby the far field pattern of the antenna system is rotated.

3. An antenna system supported by a moving platform and providing compensation for the movement of the platform, the antenna system comprising:

a first array adapted to transmit power and having an odd illumination function;

a second array adapted to transmit power, interleaved with the first array, and having an even illumination function;

variable phase shifting means connecting with the first array; and

variable power divider means adapted to receive power from a source of power, and communicating a portion of the power through the variable phase shifting means to the first array and a second portion of the power to the second array, whereby there is a displacement of the center of the sum of the odd and the even illumination functions, and whereby the far field antenna pattern of the antenna system is rotated.

4. The antenna system of claim 3 wherein the variable power divider means comprises a first and a second magic- T, and a first and a second variable phase shifter interconnecting the first and the second magic-T to vary the phase of power in one arm of the second magic-T relative to the phase of power in a second arm of the second magic-T.

5. The antenna system of claim 4 wherein the first and the second arrays each comprise edge slotted waveguides.

7 8 6. The antenna system of claim 5 wherein the odd 2,981,944 4/1961 Washburne 343-768 X illumination function comprises a sine function anc l the 3,135,959 6/1964 M an 343771 X even illumination function comprises a cosine function. HERMAN KARL SAALBACH, Primary Examiner Referen e Cite 5 S. CHATMON, 1a., Assistant Examiner UNITED STATES PATENTS U.S Cl. X R.

2,932,823 4/1960 Beck et a1 343-771 343-854 

